WEDNESDAY, Oct. 3 (HealthDay News) -- In a culture that frequently projects the message that you can never be too thin, a new study says genetic factors may make some women especially susceptible to that ideal.

Almost half of the reason some women are more likely to succumb to the pressure to be lean can be explained by differences in their genetic makeup, the new research suggests.

Some women may essentially have two risk factors: They are innately predisposed to want to be thin, and also have family members, friends or activities reinforcing thinness as an ideal, according to the study.

In other words, it's not the culture of fashion magazines, TV and film that's really the problem for women who are genetically most susceptible. Rather, for these teens and young women, their buddies, a dance class or parents who periodically call them plump compound the problem.

"Basically, we vary in how permeable we are to environmental toxins -- including media pressures about the thin ideal -- and that variation can have its roots in genes," said Cynthia Bulik, director of the University of North Carolina Eating Disorders Program, in Chapel Hill. She was not associated with this study.

The study, based on data from 2008 to 2012, examined genetic and environmental influences on what the researchers call "thin-ideal internalization," social reinforcement by people the women respect. Internalizing the "be-thin" messaging is considered a risk factor for body-image disturbances and eating disorders.

The need to be thin isn't absorbed from the larger culture by everyone, Bulik said.

"Why do some girls or women -- and even boys and men -- see a Photoshopped image or hear an advertisement that urges them to become dissatisfied with some aspect of their physical appearance and totally brush it off, whereas others go to the mirror, perform a self-evaluation, take it onboard, become self-critical, experience a plummeting of their mood and engage in disordered eating behaviors to try to correct the manufactured flaw?" she asked.

The study, published in the International Journal of Eating Disorders, involved sets of twins from the Michigan State University Twin Registry. Participants included nearly 350 females aged 12 to 22; all were born in Michigan and 80 percent were white.

The researchers measured how much the participants wanted to look like people in film, TV and magazines to gauge their level of "thin idealization." Identical twins (who share 100 percent of their genes) were compared to fraternal twins (who share 50 percent of their genes).

Identical twins had more similar levels of "thin idealization" than did fraternal twins, the research found. That suggests that genes play a role in explaining the differences between the two types of twins, the study authors said.

The study suggests that the "heritability" of thin idealization is 43 percent, meaning that almost half of the reason women are more prone to idealize thinness may be due to genetic differences, the researchers said.

The study, however, was not designed to determine a cause-and-effect relationship between genetics and thin idealization, but rather only a link.

"Some people have a genetic propensity to internalize these ideals," said Jessica Suisman, a study co-author and graduate student at Michigan State. "The broad cultural risk factors that we thought were most influential in the development of thin-ideal internalization are not as important as genetic risk and environmental risk factors that are specific and unique to each twin."

Suisman advises women who realize they idealize thinness to try to participate in social and leisure environments that put less emphasis on being lean.

"Listen for it, and avoid having some of the negative thoughts about your own body," she said. In other words, women should tell themselves they are OK as they are.

The researchers would like to expand the study to a larger number of participants with broader ethnic and cultural backgrounds, Suisman said.

"We'd also like to know if the genes affecting the risk of internalizing thinness are the same or similar to those that affect eating disorders," she said. "And we'd like to analyze personality traits -- such as perfectionism and high levels of emotion -- to see how those factors may be involved."